Plating apparatus and plating method

ABSTRACT

Provided are a plating apparatus and a plating method for preventing or mitigating electric field diversion irrespective of the physical or mechanical structure. According to one embodiment, provided is a plating apparatus comprising: a substrate holder configured so as to hold a substrate; a plating bath configured so as to accommodate the substrate holder which holds the substrate, and provided with a first tank on a first surface side of the substrate and a second tank on a second surface side of the substrate, the first tank and the second tank communicating with each other with a gap therebetween; a first anode electrode arranged in the first tank of the plating bath; a first power source configured so as to supply a plating current between the substrate and the first anode electrode; an auxiliary anode electrode arranged on the first tank side of the gap; an auxiliary cathode electrode arranged on the second tank side of the gap; and an auxiliary power source configured so as to supply an auxiliary current between the auxiliary anode electrode and the auxiliary cathode electrode.

TECHNICAL FIELD

The present invention relates to a plating apparatus and a plating method, more specifically, a technique for making plated film thickness uniform.

BACKGROUND ART

A process for forming a metal plated film, which comprises metal such as copper or the like, on a surface of a semiconductor device or a substrate for an electronic element has been practiced. For example, there is a case wherein a substrate, which is an object of plating, is held by a substrate holder, and the substrate, together with the substrate holder, is put in a plating tank to soak it in plating liquid stored in the plating tank to electroplate it. The substrate holder holds the substrate in such a manner that a to-be-plated surface of the substrate is exposed. In the plating liquid, an anode is arranged to correspond to the exposed surface of the substrate and a voltage is applied between the substrate and the anode, so that an electroplated film can be formed on the exposed surface of the substrate.

There is a substrate holder which is provided with openings on both a front side and a back side thereof for plating both surfaces of the substrate. For example, there is a substrate holder which holds a substrate in such a manner that both a front surface and a back surface of a single substrate are exposed.

In the case when a plating process is performed by using a substrate holder, such as that explained above, which is provided with openings on both a front side and a back side thereof, there may be a large gap between the substrate holder and a plating tank. In the case that there is a large gap between a substrate holder and a plating tank, sneaking of part of an electric field, that has an electric field direction from an anode to a substrate, may occur. For example, a part of an electric field, that has an electric field direction from an anode to a front surface, which faces the anode, of a substrate held by a substrate holder, may sneak up on a back surface of the substrate held by the substrate holder. If sneaking of an electric field has occur, it becomes difficult to form a plated film having uniform thickness on a substrate. Patent Literature 1 discloses a plating apparatus which is constructed to block such sneaking of an electric field by using a physical/mechanical structure.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Application Public Disclosure No. 2020-139206

SUMMARY OF INVENTION Technical Problem

An object of the present disclosure is to provide a plating apparatus and a plating method for preventing or lessening sneaking of an electric field without relying on a physical/mechanical structure.

Solution to Problem

According to an embodiment, a plating apparatus is provided, and the plating apparatus comprises: a substrate holder constructed to hold a substrate; a plating tank constructed to allow the substrate holder holding the substrate to be put in the inside thereof, and comprising a first tank positioned on the side of a first surface of the substrate and a second tank positioned on the side of a second surface of the substrate, wherein the first tank and the second tank communicate with each other via a gap; a first anode electrode arranged in the first tank in the plating tank; a first electric power source constructed to supply plating current between the substrate and the first anode electrode; an auxiliary anode electrode arranged in a position that is in the gap and on the side of the first tank; an auxiliary cathode electrode arranged in a position that is in the gap and on the side of the second tank; and an auxiliary electric power source constructed to supply auxiliary current between the auxiliary anode electrode and the auxiliary cathode electrode.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general layout drawing of a plating apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a construction of a plating tank according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing the construction of the plating tank according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing the construction of the plating tank according to the embodiment of the present invention.

FIG. 5 is a figure schematically showing plating current flowing through the inside of a plating tank according to an embodiment of the present invention.

FIG. 6 is a figure schematically showing plating current and auxiliary current flowing through the inside of a plating tank according to an embodiment of the present invention.

FIG. 7 is a figure representing an equivalent circuit corresponding to a plating tank according to an embodiment of the present invention.

FIG. 8 is a figure representing an equivalent circuit corresponding to a plating tank according to an embodiment of the present invention.

FIG. 9 is a figure representing an equivalent circuit corresponding to a plating tank according to an embodiment of the present invention.

FIG. 10 is a figure representing an equivalent circuit corresponding to a plating tank according to an embodiment of the present invention.

FIG. 11 is a figure representing an equivalent circuit corresponding to a plating tank according to an embodiment of the present invention.

FIG. 12 is a figure representing an equivalent circuit corresponding to a plating tank according to an embodiment of the present invention.

FIG. 13 is a figure showing a construction example of a part comprising a partition wall and a gap, in a plating tank according to an embodiment of the present invention.

FIG. 14 is a figure showing a different construction example of the part comprising a partition wall and a gap, in a plating tank according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

In the following description, embodiments of the present invention will be explained with reference to the figures. In the figures which will be explained below, a reference symbol assigned to one component is also assigned to the other component if the other component is the same as or corresponds to the one component, and overlapping explanation of these components will be omitted.

FIG. 1 is a general layout drawing of a plating apparatus 100 according to an embodiment of the present invention. The plating apparatus 100 is roughly divided into a load/unload module 110 which loads a substrate into a substrate holder (which is not shown in the figure) or unloads a substrate from a substrate holder, a processing module 120 which processes a substrate, and a washing module 50 a. Further, the processing module 120 comprises a pre-processing/post-processing module 120A which performs pre-processing and post-processing of a substrate, and a plating processing module 120B which applies plating processing to a substrate.

The load/unload module 110 comprises a handling stage 26, a substrate transfer device 27, and a fixing station 29. For example, in the present embodiment, the load/unload module 110 comprises two handling stages, specifically, a handling stage 26A for loading, which handles a substrate to which no process has been applied, and a handling stage 26B for unloading, which handles a substrate with respect to which a process applied thereto has been completed. In the present embodiment, the construction of the handling stage 26A for loading is the same as that of the handling stage 26B for unloading, and they are arranged in such a manner that the directions thereof are 180-degree opposite from each other. In this regard, the handling stage 26 is not limited to that comprising the handling stage 26A for loading and the handling stage 26B for unloading, and the handling stages may be used without discrimination, i.e., without setting one of them to be a handling stage for loading and the other of them to be a handling stage for unloading. Further, in the present embodiment, the load/unload module 110 comprises two fixing stations 29. The mechanisms of the two fixing stations 29 are identical with each other; and one, which is free (i.e., which is not handling a substrate), of them is used. In this regard, one or three or more handling stage/stages 26 and one or three or more fixing station/stations 29 may be installed according to the space in the plating apparatus 100.

Substrates are conveyed from plural cassette tables 25 (for example, three in FIG. 1 ) to the handling stage 26 (the handling stage 26A for loading) via a robot 24. The cassette table 25 is provided with a cassette 25 a in which a substrate is stored. For example, the cassette is a FOUP. The handling stage 26 is constructed in such a manner that it adjusts (aligns) the position and the direction of a substrate put thereon. A substrate transfer device 27 is arranged in a position between the handling stage 26 and the fixing station 29 for conveying a substrate between them. The substrate transfer device 27 is constructed to convey a substrate between the handling stage 26, the fixing station 29, and the washing module 50 a. Further, a stocker 30, which is used for storing substrate holders, is installed in a position near the fixing station 29.

The washing module 50 a comprises a washing device 50 which washes a substrate, with respect to which a plating process applied thereto has been completed, and dries it. The substrate transfer device 27 is constructed to convey a substrate, with respect to which a plating process applied thereto has been completed, to the washing device 50, and take the washed substrate out of the washing device 50. Thereafter, the washed substrate is delivered to the handling stage 26 (the handling stage 26B for unloading) by the substrate transfer device 27, and returned to the cassette 25 a via the robot 24.

The pre-processing/post-processing module 120A comprises a pre-wet tank 32, a pre-soak tank 33, a pre-rinse tank 34, a blow tank 35, and a rinse tank 36. In the pre-wet tank 32, a substrate is soaked into pure water. In the pre-soak tank 33, an oxide film on a surface of a conductive layer, such as a seed layer or the like, formed on a surface of a substrate is removed by etching. In the pre-rinse tank 34, a substrate, with respect to which a pre-soaking process applied thereto has been completed, is washed together with a substrate holder by using cleaning liquid (pure water or the like). In the blow tank 35, liquid removal of a washed substrate is performed. In the rinse tank 36, a plated substrate is washed together with a substrate holder by using cleaning liquid. In this regard, the construction of the pre-processing/post-processing module 120A in the plating apparatus 100 is a mere example, so that the construction of the pre-processing/post-processing module 120A in the plating apparatus 100 is not limited thereto, and a different construction may be adopted.

The plating processing module 120B is constructed, for example, in such a manner that plural plating tanks 39 are housed in the inside of an overflow tank 38. Each plating tank 39 is constructed in such a manner that it stores a single substrate therein, and makes the substrate be soaked into plating liquid held in the inside thereof and applies plating such as copper plating or the like to a surface of the substrate.

The plating apparatus 100 comprises a transporter 37 which adopts a linear motor system, for example, and is arranged in a position on a side of the pre-processing/post-processing module 120A and the plating processing module 120B for conveying a substrate holder together with a substrate. The transporter 37 is constructed to convey a substrate holder between the fixing station 29, the stocker 30, the pre-wet tank 32, the pre-soak tank 33, the pre-rinse tank 34, the blow tank 35, the rinse tank 36, and the plating tank 39.

An example of a series of plating processes performed by the plating apparatus 100 will be explained. First, by the robot 24, a single substrate is taken out of the cassette 25 a loaded in the cassette table 25; and the substrate is conveyed to the handling stage 26 (the handling stage 26A for loading). The handling stage 26 aligns the position and the direction of the conveyed substrate with a predetermined position and a predetermined direction. The substrate, with respect to which the position and the direction have been aligned in the handling stage 26, is conveyed to the fixing station 29 by the substrate transfer device 27.

On the other hand, a substrate holder stored in the stocker 30 is conveyed to the fixing station 29 by the transporter 37, and put horizontally on the fixing station 29. Thereafter, the substrate conveyed by the substrate transfer device 27 is put on the substrate holder which is in the above state, and the substrate and the substrate holder are coupled with each other.

Next, the substrate holder, which holds the substrate, is grasped by the transporter 37 to store it in the pre-wet tank 32. Next, the substrate holder, which holds the substrate with respect to which the process applied thereto in the pre-wet tank 32 has been completed, is conveyed to the pre-soak tank 33 by the transporter 37, to etch an oxide film on the substrate in the pre-soak tank 33. Following thereto, the substrate holder, which holds the above substrate, is conveyed to the pre-rinse tank 34 to water-wash the surface of the substrate by pure water stored in the pre-rinse tank 34.

The substrate holder, which holds the substrate, with respect to which the water-washing process applied thereto has been completed, is conveyed from the pre-rinse tank 34 to the plating processing module 120B by the transporter 37 to store it in the plating tank 39 which is filled with plating liquid. The transporter 37 repeats the above procedures sequentially to store respective substrate holders, which hold respective substrates, in respective plating tanks 39 in the processing module 120 sequentially.

In each of the plating tanks 39, a surface of the substrate is plated by applying a plating voltage between an anode (which is not shown in the figure) in the plating tank 39 and the substrate.

After completion of plating, the substrate holder, which holds the plated substrate, is grasped by the transporter 37 and conveyed to the rinse tank 36 to soak it into pure water stored in the rinse tank 36 to wash the surface of the substrate by the pure water. Next, the substrate holder is conveyed to the blow tank 35 by the transporter 37 to remove water droplets remaining on the substrate holder by air-blowing or the like. Thereafter, the substrate holder is conveyed to the fixing station 29 by the transporter 37.

In the fixing station 29, the processed substrate is taken out of the substrate holder by the substrate transfer device 27, and conveyed to the washing device 50 in the washing module 50 a. The washing device 50 washes and dries the substrate, with respect to which the plating process applied thereto has been completed. The dried substrate is delivered to the handling stage 26 (the handling stage 26B for unloading) by the substrate transfer device 27, and returned to the cassette 25 a via the robot 24.

Each of FIGS. 2-4 is a schematic diagram showing a construction of one of plating tanks 39 in the plating processing module 120B. FIG. 3 shows a section view, that is viewed in a direction of an arrow A, of the plating tank 39 cut along an A-A plane in FIG. 2 ; and FIG. 4 shows a section view, that is viewed in a direction of an arrow B, of the plating tank 39 cut along an B-B plane in FIG. 2 . Each of the plating tanks 39 in the plating processing module 120B has a construction that is the same as that shown in each of FIGS. 2-4 .

As explained above, the substrate holder 30, which is holding a substrate W, is conveyed by the transporter 37 (refer to FIG. 1 ) to be stored in the plating tank 39. In the plating tank 39, the substrate W and the substrate holed 30 are soaked in a plating liquid (electrolytic solution). A horizontal line QS shown in each of FIGS. 3 and 4 represents a liquid surface of a plating liquid Q. A partition wall 39 a is installed on an inner wall and an inner bottom of the plating tank 39 in such a manner that it is arranged in parallel with a surface of the substrate W and on a plane that is the same as that on which the substrate W and the substrate holder 30 are arranged. The partition wall 39 a, together with the substrate W and the substrate holder 30, partitions the inside of the plating tank 39 into two parts, i.e., a first tank 39-1 and a second tank 39-2.

An end part of one side of the partition wall 39 a is connected with the inner wall and the inner bottom of the plating tank 39 (for example, the partition wall 39 a and the inner wall and the inner bottom of the plating tank 39 are connected with one another without any gaps). On the other hand, there is a gap GP between an end part of the other side of the partition wall 39 a and a circumference of the substrate holder 30. For example, the substrate holder 30 may be supported or suspended by a supporting mechanism, which is not shown in the figures, in such a manner that it does not come in contact with the partition wall 39 a, so that the gap GP such as that shown in each of FIGS. 3 and 4 may be formed around the whole circumference of the substrate holder 30. In a different example, the partition wall 39 a may have a shape such that a part(s) of the partition wall 39 a may come in contact with the substrate holder 30, and, in such a case, the gap(s) GP may partly be formed around a part(s) of the circumference of the substrate holder 30.

Due to a gap such as the gap GP existing in the position between the substrate holder 30 and the partition wall 39 a in the plating tank 39, the first tank 39-1 and the second tank 39-2 in the plating tank 39 are not completely separated from each other. In other words, the first tank 39-1 in the plating tank 39 communicates with the second tank 39-2 via the gap GP, so that the plating liquid Q and ions included in the plating liquid Q can move between the first tank 39-1 and the second tank 39-2 via the gap GP.

A first anode electrode 221, which is held by an anode holder which is not shown in the figures, is arranged in the first tank 39-1 in the plating tank 39. The first anode electrode 221 is electrically connected to a positive electrode of a first electric power source 231, and a negative electrode of the first electric power source 231 is electrically connected to a surface (hereinafter, a first surface W1), which faces toward a first tank 39-1 side, of the substrate W. Conductive material such as a seed layer or the like may be formed on the first surface W1 of the substrate W. The first electric power source 231 is constructed to supply plating current between the first anode electrode 221 and the first surface W1 of the substrate W.

Similarly, a second anode electrode 222, which is held by an anode holder which is not shown in the figures, is arranged in the second tank 39-2 in the plating tank 39. The second anode electrode 222 is electrically connected to a positive electrode of a second electric power source 232, and a negative electrode of the second electric power source 232 is electrically connected to a surface (hereinafter, a second surface W2), which faces toward a second tank 39-2 side, of the substrate W. Conductive material such as a seed layer or the like may be formed on the second surface W2 of the substrate W. The second electric power source 232 is constructed to supply plating current between the second anode electrode 222 and the second surface W2 of the substrate W.

FIG. 5 is a figure which schematically represents plating current flowing through the plating liquid Q in the first tank 39-1 and the second tank 39-2 in the plating tank 39. In the first tank 39-1, the plating current flows from the first anode electrode 221 to the first surface W1 of the substrate W as shown by arrows IQ1; and, in the second tank 39-2, the plating current flows from the second anode electrode 222 to the second surface W2 of the substrate W as shown by arrows IQ2. In this regard, if the first surface W1 and the second surface W2 of the substrate W are electrically conducted with each other within the substrate (for example, if the first surface W1 and the second surface W2 of the substrate W are electrically conducted with each other by a via), an electric current path comprising the gap GP between the substrate holder 30 and the partition wall 39 a of the plating tank 39, through which electric current flows, may be formed in the plating tank 39. For example, if current density in the plating liquid Q in the first tank 39-1 is larger than current density in the plating liquid Q in the second tank 39-2, current that sneaks up on the side of the second tank 39-2 from the side of the first tank 39-1 via the gap GP is formed as shown by arrows IQ12 in FIG. 5 . In the case that the relationship in terms of the magnitude of the current density is that opposite to the above relationship, the current leaks from the second tank 39-2 to the first tank 39-1 unlike the case shown in FIG. 5 ; however, in the following description, the state that is to be considered when providing explanation will be a state such as that shown in FIG. 5 .

The plating apparatus 100 according to the present embodiment comprises an auxiliary anode electrode 241 and an auxiliary cathode electrode 242 in the plating tank 39, for reducing or preventing sneaking of current such as that explained above. The auxiliary anode electrode 241 is installed in a position that is close to the gap GP and is on a surface, on a first tank 39-1 side, of the partition wall 39 a, as shown in FIGS. 2 and 3 . Further, the auxiliary cathode electrode 242 is installed in a position that is close to the gap GP and is on a surface, on a second tank 39-2 side, of the partition wall 39 a, as shown in FIGS. 2 and 4 . Each of the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 may be that arranged in a position along the whole of a circumference of the gap GP formed between the substrate holder 30 and the partition wall 39 a, as shown in each of FIGS. 3 and 4 . In this regard, adoption of the above arrangement is not necessarily required; so that, for example, one of or both the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 may be arranged only in a position along a part of the gap GP, or may be arranged in such a manner that it/they may be divided into plural parts along the gap GP.

The auxiliary anode electrode 241 is electrically connected to a positive electrode of an auxiliary electric power source 243, and the auxiliary cathode electrode 242 is electrically connected to a negative electrode of the auxiliary electric power source 243. The auxiliary electric power source 243 is constructed to supply auxiliary current between the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 via the gap GP. FIG. 6 is a figure which schematically represents plating current and auxiliary current flowing through the inside of the plating tank 39; and, as shown in the figure, the auxiliary current flows from the side of the first tank 39-1 to the side of the second tank 39-2 (arrows IQ3), in the gap GP part between the substrate holder 30 and the partition wall 39 a. Further, on the outer side of the gap GP, the auxiliary current flows toward the first surface W1 of the substrate W from the auxiliary anode electrode 241 (arrows IQ31), and also flows toward the auxiliary cathode electrode 242 from the second anode electrode 222 (arrows IQ32). Since each of the directions of the components IQ31 and IQ32 of the auxiliary current is opposite to the direction of the sneaking component IQ12 of the plating current, one component weakens the other component or the both components negate each other; so that the net quantity of the flow of the current from the first tank 39-1 to the second tank 39-2 (i.e., sneaking of the plating current) can be reduced, or flowing of the current can be prevented. In the following description, matters relating to the optimum magnitude of the auxiliary current that can negate the plating current sneaking up on the second tank 39-2 from the first tank 39-1 via the gap GP will be explained.

Each of FIGS. 7 and 8 is a figure representing an equivalent circuit corresponding to the plating tank 39 in the plating apparatus 100 according to the present embodiment. The equivalent circuit shows relationship with respect to connection between respective elements shown in FIG. 2 , i.e., shows how the respective elements are electrically connected with one another. In the two figures, FIG. 7 is an equivalent circuit in which some elements relating to the auxiliary current are omitted for convenience of explanation and understanding, and FIG. 8 shows a complete equivalent circuit comprising elements relating to the auxiliary current.

With reference to FIG. 7 , polarization resistance in the first anode electrode 221 is denoted as RA1, resistance of the plating liquid Q in a region between the first anode electrode 221 and the first surface W1 of the substrate W is denoted as RE1, polarization resistance in the first surface W1 of the substrate W (i.e., the cathode) is denoted as RC1, resistance in the first surface W1 (for example, a seed layer thereon) of the substrate W is denoted as RS1, resistance of the plating liquid Q in a region from an opening on the side of the first tank 39-1 to an opening on the side of the second tank 39-2 of the gap GP is denoted as RIC, internal interconnection resistance of a region (for example, a via) connecting the first surface W1 and the second surface W2 of the substrate W with each other is denoted as RIS, polarization resistance in the second anode electrode 222 is denoted as RA2, resistance of the plating liquid Q in a region between the second anode electrode 222 and the second surface W2 of the substrate W is denoted as RE2, polarization resistance in the second surface W2 of the substrate W (i.e., the cathode) is denoted as RC2, and resistance in the second surface W2 (for example, a seed layer thereon) of the substrate W is denoted as RS12. Further, output current from the first electric power source 231 is denoted as I1; current, in I1, flowing to the first surface W1 of the substrate W is denoted as I1-1; current, in I1, flowing to the side of the second tank 39-2 through the gap GP is denoted as I1-2; output current from the second electric power source 232 is denoted as I2; current, in I2, flowing to the second surface W2 of the substrate W is denoted as I2-1; and current, in I2, flowing to the side of the first tank 39-1 through the gap GP is denoted as I2-2. In this regard, I1=I1-1+I1-2 and I2=I2-1+I2-2.

In the above case, in a closed circuit C shown in FIG. 7 , the following formula can be established based on the law of Kirchhoff:

VC1=VC2+(RIC+RIS)·(I1-2−I2-2)  (1)

In this regard, it is supposed that VC1 and VC2 are over-voltages of cathode reaction (reduction reaction) in the first surface W1 and the second surface W2 of the substrate W, respectively, and that there is relationship such as VC1>VC2. Further, since an over-voltage is proportional to current in the case that the over-voltage is small, the over-voltages can be represented as VC1=RC1·(I1-1+I2-2) and VC2=RC2·(I2-1+I1-2).

Next, as shown in FIG. 8 , the auxiliary current Iaux is supplied from the auxiliary electric power source 243 via the auxiliary anode electrode 241 and the auxiliary cathode electrode 242. In Iaux, the current flowing from the auxiliary anode electrode 241 to the first surface W1 of the substrate is denoted as Iaux-1, and the current flowing from the auxiliary anode electrode 241 to the second tank 39-2 via the gap GP is denoted as Iaux-2. In this regard, Iaux=Iaux-1+Iaux-2. In this case, the current flowing into the gap GP from the first tank 39-1 (and the current flowing out of the gap GP to the second tank 39-2) can be represented as I1-2-I2-2-Iaux-1, and, if the current is zero, net flowing of current from the first tank 39-1 to the second tank 39-2 does not occur. That is, the condition for negating, by using the auxiliary current Iaux, the plating current sneaking up on the second tank 39-2 side from the first tank 39-1 side via the gap GP is represented by the following formula:

I1-2−I2-2=Iaux-1  (2)

If the above condition is satisfied, the current in respective parts of the equivalent circuit in FIG. 8 can be represented as those in an equivalent circuit shown in FIG. 9 . Similar to the case of above formula (1), the following formula can be established with respect to a closed circuit C in FIG. 9 , based on the law of Kirchhoff:

VC1−VC2=RIC·Iaux  (3)

Thus, by setting the auxiliary current Iaux in such a manner that it satisfies formula (3), that is, by setting the auxiliary current Iaux to a value obtained by dividing a difference between the over-voltage VC1 in the first surface W1 and the over-voltage VC2 in the second surface W2 in the substrate W by a value RIC of resistance between the auxiliary anode electrode 241 and the auxiliary cathode electrode 242, sneaking of the plating current from the first tank 39-1 side to the second tank 39-2 side via the gap GP can be prevented. In other words, the optimum value of the auxiliary current Iaux for preventing sneaking of the plating current can be represented as (VC1−VC2)/RIC. Formula (3) shows the optimum value of the auxiliary current Iaux; however, it is possible to reduce, to a certain extent, sneaking of the plating current even if the value of the auxiliary current slightly deviates from the above optimum value.

Regarding formula (3), the values of the over-voltage VC1 in the first surface W1 and the over-voltage VC2 in the second surface W2 in the substrate W can be obtained by: measuring, by using reference electrodes (potential measuring probes) arranged in positions close to the first surface W1 and the second surface W2, respectively, in the substrate W, equilibrium potential at the time when plating current is not being applied and potential at the time when plating current is being applied and reaction is being occurred; and, based on difference between the equilibrium potential and the potential during reaction, determining respective over-voltages. Regarding the over-voltages VC1 and VC2, each of the vales thereof may be that obtained in advance by measuring potential with respect to a test substrate, and the values may be used permanently; or each of the over-voltages VC1 and VC2 in real time may be calculated by using values of potential measured in real time with respect to a substrate which is to be used in an actual product, and the auxiliary current Iaux may be adjusted in real time by using the above over-voltages.

Further, the value RIC of resistance between the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 in formula (3) can be calculated, for example, by using the size of the gap GP and the electric conductivity of the plating liquid Q.

In the case that the over-voltages VC1 and VC2 are small, the over-voltages are proportional to current, so that formula (3) can be modified to that shown below. In this regard, each of Rp1 and Rp2 is polarization resistance per unit area, and each of i1 and i2 is current density.

$\begin{matrix} {Iaux} & {= {\left( {{{RC}{1 \cdot I}1} - {{RC}{2 \cdot I}2}} \right)/{RIC}}} & (4) \\  & {= {\left( {{{Rp}{1 \cdot i}1} - {{Rp}{2 \cdot i}2}} \right)/{RIC}}} & \left( 4^{\prime} \right) \end{matrix}$

Further, regarding the case that values of the polarization resistance per unit area, Rp1 and Rp2, are equal to each other, if it is defined that Rp=Rp1=Rp2, formula (4′) becomes that shown below:

Iaux=Rp/RIC·(i1−i2)  (5)

Thus, by using formula (4) or (5), the optimum value of the auxiliary current Iaux can be determined based on measured values of current I1 and I2 or current density i1 and i2. In this regard, in formulas (4) and (5), each of the values of polarization resistance RC1, RC2, and Rp can be derived from an IV curve that is obtained in advance from measurement using a reference electrode, for example.

In the above explanation, it is supposed that the current I1 is outputted from the first electric power source 231 and the current I2 is outputted from the second electric power source 232; however, it is possible to consider the case that the output current from the second electric power source 232 is zero (that is, I2=I2-1=I2-2=0). For example, outputting from the second electric power source 232 may be stopped simply, or the second electric power source 232 and the second anode electrode 222 themselves may be omitted from the plating tank 39. The plating apparatus 100 according to the present embodiment can be applied even in the case such as that explained above, i.e., the case wherein a plating process is applied to a single surface (the first surface W1) of the substrate W only.

Each of FIGS. 10-12 is a figure representing an equivalent circuit corresponding to the plating tank 39 when output current from the second electric power source 232 is zero; and FIGS. 10-12 correspond to above-explained FIGS. 7-9 , respectively. In the present case, above formulas (1), (2), (3), (4), and (5) become following formulas (6), (7), (8), (9), and (10), respectively:

VC1=VC2+(RIC+RIS)·I1-2  (6)

I1-2=Iaux-1  (7)

VC1=RIC·Iaux  (8)

Iaux=RC1·I1/RIC  (9)

Iaux=Rp1/RIC·i1  (10)

Accordingly, in the case that output current from the second electric power source 232 is zero, sneaking of the plating current from the first tank 39-1 side to the second tank 39-2 side via the gap GP can be prevented by setting the auxiliary current Iaux in accordance with above formula (8), (9), or (10).

FIG. 13 is a figure which shows a construction example of a part comprising the partition wall 39 a and the gap GP, in the plating tank 39 in the plating apparatus 100 according to the present embodiment. In the example in FIG. 13 , the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 are arranged in such a manner that they are put in recesses of the partition wall 39 a and fixed to bus bars 245, respectively. The recesses of the partition wall 39 a are provided with barrier membranes 246; and the inside spaces of the recesses, in which the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 are put, and the first tank 39-1 and the second tank 39-2 in the plating tank 39 are partitioned from one another by the barrier membranes 246, respectively. The barrier membrane 246 is a membrane which has a function to selectively allow permeation of specific ions.

By separating the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 from the first tank 39-1 and the second tank 39-2 by the barrier membranes 246, respectively, diffusion of metal ions or fine particles, which are to be eluted from the auxiliary anode electrode 241 and the auxiliary cathode electrode 242 if they are soluble electrodes, into the first tank 39-1 and the second tank 39-2 in the plating tank 39 can be suppressed. In the case that the auxiliary anode electrode 241 is an insoluble electrode, diffusion of active oxygen, that are to be generated by the auxiliary cathode electrode 242, into the first tank 39-1 can be suppressed.

The liquid that fills the inside space of the recess may be an electrolytic solution that is different from the plating liquid Q. In such a case, deposition of metal onto the auxiliary anode electrode 241 can be suppressed or prevented. Further, in the case that additives are included in the plating liquid Q, movement of the additives toward the auxiliary anode electrode 241 side and the auxiliary cathode electrode 242 side and decomposition of the moved additives on the electrode surfaces can be prevented.

FIG. 14 is a figure which shows a different construction example of the part comprising the partition wall 39 a and the gap GP, in the plating tank 39 in the plating apparatus 100 according to the present embodiment. In the example in FIG. 14 , the substrate holder 30 is constructed to have a shape having a protruding part on a surface facing the partition wall 39 a, and the partition wall 39 a in the plating tank 39 is constructed to have a shape having a depression on a surface facing the substrate holder 30. As a result that the protruding part of the substrate holder 30 and the depression of the partition wall 39 a are joined together, the gap GP between the substrate holder 30 and the partition wall 39 a is formed as a bent path between the first tank 39-1 and the second tank 39-2 in the plating tank 39.

Due to the bent path, the distance between the first tank 39-1 and the second tank 39-2, i.e., the distance that each ion moves, becomes long, so that the value RIC of the resistance of the plating liquid Q in the gap GP increases. In this regard, the optimum value of the auxiliary current Iaux that can prevent sneaking of the plating current is inversely proportional to RIC, according to above-explained formulas (3)-(5) and (8)-(10); so that the optimum value of the auxiliary current Iaux can be made small and the electric power required for preventing sneaking of the plating current can be reduced consequently, by making the gap GP have a construction such as that of the bent path explained above.

In the above description, embodiments of the present invention have been explained based on some examples; and, in this regard, the above explained embodiments of the present invention are those used for facilitating understanding of the present invention, and are not those used for limiting the present invention. It is obvious that the present invention can be changed or modified without departing from the scope of the gist thereof, and that the present invention includes equivalents thereof. Further, it is possible to arbitrarily combine components or omit a component(s) disclosed in the claims and the specification, within the scope that at least part of the above-stated problems can be solved or within the scope that at least part of advantageous effect can be obtained. 

1. A plating apparatus comprising: a substrate holder constructed to hold a substrate; a plating tank constructed to allow the substrate holder holding the substrate to be put in the inside thereof, and comprising a first tank positioned on the side of a first surface of the substrate and a second tank positioned on the side of a second surface of the substrate, wherein the first tank and the second tank communicate with each other via a gap; a first anode electrode arranged in the first tank in the plating tank; a first electric power source constructed to supply plating current between the substrate and the first anode electrode; an auxiliary anode electrode arranged in a position that is in the gap and on the side of the first tank; an auxiliary cathode electrode arranged in a position that is in the gap and on the side of the second tank; and an auxiliary electric power source constructed to supply auxiliary current between the auxiliary anode electrode and the auxiliary cathode electrode.
 2. The plating apparatus according to claim 1, wherein the auxiliary current is set to have a current value that is obtained by dividing an over-voltage in the first surface of the substrate by a resistance value of electrolytic solution that exists between the auxiliary anode electrode and the auxiliary cathode electrode.
 3. The plating apparatus according to claim 1 further comprising: a second anode electrode arranged in the second tank in the plating tank; and a second electric power source constructed to supply plating current between the substrate and the second anode electrode, wherein current outputted from the second electric power source is set in such a manner that an over-voltage in the second surface of the substrate is smaller than an over-voltage in the first surface of the substrate.
 4. The plating apparatus according to claim 3, wherein the auxiliary current is set to have a current value that is obtained by dividing a difference between the over-voltage in the first surface of the substrate and the over-voltage in the second surface of the substrate by a resistance value of electrolytic solution that exists between the auxiliary anode electrode and the auxiliary cathode electrode.
 5. The plating apparatus according to claim 4 further comprising: a first reference electrode, which is arranged in a position close to the first surface of the substrate, for measuring an over-voltage in the first surface of the substrate, and a second reference electrode, which is arranged in a position close to the second surface of the substrate, for measuring an over-voltage in the second surface of the substrate; wherein the auxiliary current is controlled based on an over-voltage measured by using the first reference electrode and an over-voltage measured by using the second reference electrode.
 6. The plating apparatus according to claim 4, wherein the auxiliary current is controlled based on a measured value of current supplied from the first electric power source and a measured value of current supplied from the second electric power source.
 7. The plating apparatus according to claim 6, wherein the auxiliary current is controlled based on a difference between current density in the first surface of the substrate and current density in the second surface of the substrate.
 8. The plating apparatus according to any one of claim 7 comprising barrier membranes arranged in a position between the auxiliary anode electrode and the first tank in the plating tank and a position between the auxiliary cathode electrode and the second tank in the plating tank, and constructed to allow selective permeation of ions.
 9. The plating apparatus according to any one of claim 8, wherein the gap makes the first tank and the second tank communicate with each other by a bent path.
 10. The plating apparatus according to any one of claim 9, wherein the substrate is that in which the first surface and the second surface are electrically conducted to each other.
 11. A method for plating a substrate by a plating apparatus, wherein the plating apparatus comprises a substrate holder constructed to hold a substrate, and a plating tank constructed to allow the substrate holder holding the substrate to be put in the inside thereof, and comprising a first tank positioned on the side of a first surface of the substrate and a second tank positioned on the side of a second surface of the substrate, wherein the first tank and the second tank communicate with each other via a gap; and the method comprises: supplying, from a first electric power source, plating current between a first anode electrode, which is arranged in the first tank in the plating tank, and the substrate; and supplying, from an auxiliary electric power source, auxiliary current between an auxiliary anode electrode, which is arranged in a position that is in the gap and on the side of the first tank, and an auxiliary cathode electrode, which is arranged in a position that is in the gap and on the side of the second tank. 